System and Method for Off-Track Write Prevention and Data Recovery in Multiple Head Optical Tape Drives

ABSTRACT

In an optical tape drive having optical heads for writing data in tracks on an optical tape, each track having an off-track threshold, a system and method are disclosed for off-track write prevention. The system includes multiple actuators, each actuator configured to control a position of an associated optical heads. The system also includes a controller configured to determine a position of each of the optical heads relative to an associated track on the optical tape and to prevent, in response to an event causing an optical heads to have a position outside the off-track threshold of the associated track, only that optical head from writing data to the optical tape and to buffer a stream of data for that optical head for later processing.

TECHNICAL FIELD

The following relates to a system and method for off-track writeprevention and data recovery in optical tape drives having multipleoptical read and/or write heads.

BACKGROUND

Data storage tape devices with multiple heads generally utilizemethodologies that rely on the limiting margins of the data track layouton the media to prevent off-track (OT) writing of data to the media.Such limiting margins determine OT thresholds, which are monitored by aservo subsystem of the tape device that controls the common motion ofthe multiple heads. Using such thresholds, the servo subsystem preventsthe read/write channel of the device from writing data tracks too closeto each other on the media. Writing of data to the media commences,continues or resumes only if and when the servo subsystem is capable ofmoving the recording heads within the allowed thresholds.

Present multiple head designs in these tape devices include a rigid bodyhousing and actuating structure. As a result, in the event of excessiveexternal disturbances to the heads or excessive instantaneous lateralmotion of the tape media, all heads move away from the center of theircorresponding tracks and beyond the OT threshold limits. In suchcircumstances, servo off-track functionality normally invokes thebuffering of data streaming to the heads and prevents the heads fromprocessing and recording that streaming data on the tape media until allheads are moved back to within their OT threshold limits.

Tape devices with very high track densities, such as optical tapedrives, inherently have extreme and stringent requirements on off-trackthreshold margins and limits. As a result, the performance limitationsdescribed above resulting from excessive external disturbances to theheads or excessive instantaneous tape lateral motion can havesignificant adverse impact on data capacity and transfer rate of suchtape devices.

Thus, there exists a need for an improved system and method foroff-track write prevention and data recovery in an optical tape drivehaving multiple optical heads. Such a system and method would overcomeperformance limitations associated with excessive external disturbancesto optical heads or excessive instantaneous tape lateral motion toprovide greater data transfer rates overall and increased data capacity.

SUMMARY

According to one embodiment disclosed herein, in an optical tape drivecomprising a plurality of optical heads for writing data in a pluralityof tracks on an optical tape, each track having an off-track threshold,a system is provided for off-track write prevention. The systemcomprises a plurality of actuators, each actuator configured to controla position of one of the plurality of optical heads associatedtherewith. The system also comprises a controller configured todetermine a position of each of the optical heads relative to anassociated track on the optical tape and to prevent, in response to anevent causing at least one of the plurality of optical heads to have aposition outside the off-track threshold of the associated track, onlythe at least one optical head from writing data to the optical tape andto buffer a stream of data for the at least one optical head for laterprocessing.

According to another embodiment disclosed herein, in an optical tapedrive comprising a plurality of optical heads for reading data from aplurality of tracks on an optical tape, each track having an off-trackthreshold, a system is provided for off-track data recovery. The systemcomprises a plurality of actuators, each actuator configured to controla position of one of the plurality of optical heads associatedtherewith. The system also comprises a controller configured todetermine a position of each of the optical heads relative to anassociated track on the optical tape and to permit, in response to anevent causing at least one of the plurality of optical heads to have aposition outside the off-track threshold of the associated track, the atleast one optical head to stream data read from the optical tape when aloss of data from the at least one head is correctable.

According to still another embodiment disclosed herein, in an opticaltape drive comprising a plurality of optical heads for writing data in aplurality of tracks on an optical tape, each track having an off-trackthreshold, a method is provided for off-track write prevention. Themethod comprises controlling the plurality of optical heads via aplurality of actuators, each actuator configured to control a positionof one of the plurality of optical heads associated therewith, anddetermining a position of each of the optical heads relative to anassociated track on the optical tape. The method also comprisespreventing, in response to an event causing at least one of theplurality of optical heads to have a position outside the off-trackthreshold of the associated track, only the at least one optical headfrom writing data to the optical tape.

A detailed description of these embodiments and accompanying drawings isset forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a perspective view of a portion of an optical tape drivesystem with multiple optical heads and a common servo subsystemactuator;

FIG. 1 b is a magnified view of the portion of the optical tape drivesystem of

FIG. 1 a;

FIG. 2 is a perspective view of a portion of an optical tape drivesystem with multiple optical heads and multiple individual headactuators, and including an embodiment of a system for off-track writeprevention as described herein;

FIG. 3 is a perspective view of a portion of an optical tape drivesystem with multiple optical heads and multiple individual headactuators, and including an embodiment of a system for data recovery asdescribed herein;

FIG. 4 is a simplified flowchart depicting an embodiment of a method foroff-track write prevention and/or data recovery as described herein.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

With reference to FIGS. 1 a-4, a system and method for off-track writeprevention and data recovery in an optical tape drive with multipleoptical heads will be described. For ease of illustration and tofacilitate understanding, like reference numerals have been used hereinfor similar components and features throughout the drawings.

As previously discussed, data storage tape devices with multiple headsgenerally utilize an “Off Track Write” prevention methodology based onoff-track boundary thresholds determined by the limiting margins of thedata track layouts on the media. These thresholds, monitored by thedevice servo subsystem that controls the common motion of multipleheads, prevent the device read/write channel from writing data trackstoo close to each other. If and when the servo system is capable ofmoving the recording heads within the allowed thresholds, then thewriting of the data is resumed.

Referring now to FIG. 1 a, a perspective view is shown of a portion ofan optical tape drive system (10) with multiple optical heads (12) and acommon servo subsystem actuator (14). It should be noted here that theheads (12) and actuator (14) are depicted symbolically for ease ofillustration. As seen in FIG. 1 a, the multiple head design of theoptical tape device (10) include a rigid body housing (16) and actuatingstructure (14). As also seen therein, each of the multiple heads (12)function to write data to (and/or read data from) an associated datatrack (18) on the tape media (20). In that regard, the common actuator(14) moves the plurality of multiple optical heads (12) together inresponse to control signals from a controller (26).

FIG. b is a magnified view of the portion of the optical tape drivesystem (10) of FIG. 1 a. As seen therein, each data track (18) on thetape media (20) includes off-track thresholds (22). As previouslydescribed, the thresholds (22) define limits within which the multipleheads (12) are to write data to the data tracks (18) of the tape media(20).

However, as a result of the rigid body housing (16) and actuator (14),excessive external disturbances to the heads (12) or excessiveinstantaneous lateral motion of the tape media (20) causes all heads(12) to move in unison away from the center of their correspondingtracks (18) and beyond the OT threshold limits (22), as illustrated inFigure lb by the motion traces (24) showing various positions of theheads (12) over a period of time. In that event, servo off-trackfunctionality normally invokes the buffering of data streaming to theheads (12) and prevents the heads (12) from processing and recordingthat streaming data to the data tracks (18) of the tape media (20) untilall heads (12) are moved back to within their OT threshold limits (22).

As previously described, tape devices with very high track densities,such as optical tape drives, inherently have extreme and stringentrequirements on off-track threshold margins and limits. As a result, theperformance limitations described above resulting from excessiveexternal disturbances to the heads or excessive instantaneous tapelateral motion can have significant adverse impact on data capacity andtransfer rate of such tape devices. Thus, there exists a need for animproved system and method for off-track write prevention and datarecovery in an optical tape drive having multiple optical heads. Such asystem and method would overcome performance limitations described aboveto provide greater data transfer rates overall and increased datacapacity.

Referring now to FIG. 2, a perspective view is shown of a portion of anoptical tape drive system (10′) with multiple optical heads (12) andmultiple individual head actuators (14′), and including an embodiment ofa system for off-track write prevention. Once again, it should be notedthat the heads (12) and actuators (14′) are depicted symbolically forease of illustration, and that any type of optical heads and/or actuatormay be employed in connection with the various embodiments of the systemand method described herein.

FIG. 2 illustrates a multiple head data recording system (10′), whereeach recoding head (12) has an independent actuating structure (14′)associated therewith. The individual actuating structures (14′) may becontrolled by control signals from a controller (26′). Alternative, theactuating structures (14′) may be controlled by control signals fromassociated dedicated controllers or control systems (not shown). In thatregard, it should be noted that the controller (26′) may comprise anynumber or type of components, such as an appropriately programmedmicroprocessor or any other type of hardware, software or combinationthereof.

The system and method described herein for optical tape drives provideimproved detection and prevention of Off-Track data processing.According to the various embodiments of such a system and method,because of the independent motion of the recording heads (12), in theevent of an excessive external disturbance to the system (10′) orexcessive instantaneous substantially lateral motion of the tape media(20) (such as in the direction of the arrow (A) shown in FIG. 2), only asubset of the total number of heads (12) may move outside the Off-Tracklimits (22).

This is illustrated in FIG. 2 by the motion traces (24′) showing variouspositions of the heads (12) over a period of time in response to anevent (e.g., excessive external disturbance to the system (10′) orexcessive instantaneous substantially lateral motion of the tape media(20)). As seen therein, during that time period, some of the heads (12)remain within the OT limits (22) of their associated data tracks (18),while other heads (12) move outside associated OT limits (22).

The system and method described herein provide for off-track dataprocessing in cases associated with a write data process, a read dataprocess, and data recover in catastrophic failure conditions. Moreparticularly, according to the system and method described herein, in awrite data process, only the heads outside the threshold limits areprevented from writing data on their associated tracks, and associateddata is buffered for later processing. The device transfer rate and themedia capacity are therefore only marginally impacted, as compared tothe case where all heads are disabled for a period of time and all datais written later. Moreover, according to the system and method describedherein, for steaming data, a smaller buffer size and a lower number ofsequential flushing (stopping the input streaming data) are required,thereby providing for an improved data transfer rate and greater mediacapacity.

In the case of a read data process, once again, only the heads outsidethe associated OT thresholds are incapable of retrieving data. If thedistributed Error Correction Code (ECC) design in the devices is capableof correcting the loss of data from the subset of heads momentarilyoutside the OT thresholds, then streaming data retrieval may continuewithout the need for rewinding the tape. This provides greatly enhancedperformance compared to the case where all data from all heads areirretrievable for a given period of time.

In the case of data recovery in catastrophic failure conditions, becausethe system and method described herein provide functional independenceof the heads in the optical tape drive, previously written data maystill be recovered in the event of one or more head failures and/ormedia defects. Referring now to FIG. 3, a perspective view is shown of aportion of an optical tape drive system with multiple optical heads andmultiple individual head actuators, and including an embodiment of asystem for data recovery as described herein.

More specifically, as seen in FIG. 3, any head or number of heads (12)may be moved from designated but defective media tracks and/or zoneareas (30) to other tracks and/or zones (18), including a track and/orzone of a detected failed head (12′). This approach is especially usefulin the event that all the allowable number of heads recoverable by thechannel ECC have failed, and any defect in the zones of remainingoperative heads would normally results in unrecoverable read failure. Insuch am event , according to the system and method described herein, thehead or heads (12) from the defective area zones (30) may be moved tothe zones (18) of failed heads (12′) such that, by the help of thechannel ECC, the data may still be recovered under an otherwisecatastrophic failure condition.

With continuing reference to FIGS. 2 and 3, in an optical tape drivecomprising a plurality of optical heads (12) for writing data in aplurality of tracks (18) on an optical tape (20), each track (18) havingan off-track threshold (22), a system is shown for off-track writeprevention and/or data recovery. The system may comprise a plurality ofactuators (14′), each actuator (14′) configured to control a position ofone of the plurality of optical heads (12) associated therewith. Thesystem may further comprise a controller (26′) configured to determine aposition of each of the optical heads (12) relative to an associatedtrack (18) on the optical tape (20) and to prevent, in response to anevent causing at least one of the plurality of optical heads (12) tohave a position outside the off-track threshold (22) of the associatedtrack (18), only that optical head or heads (12) from writing data tothe optical tape (20) and to buffer a stream of data for that opticalhead or heads (12) for later processing.

As previously described, the event may be a disturbance external to theoptical tape drive and/or motion of the optical tape (20) in a directionsubstantially lateral to a direction of tape travel (shown by arrow(B)). Moreover, the controller (26′) may be further configured topermit, in response to the event, an optical head (12) to write data tothe optical tape (20) as long as the optical head (12) has a positionwithin the off-track threshold (22) of the associated track (18).

The optical tape drive may further comprises a plurality of opticalheads (12) for reading data from a plurality of tracks (18) on theoptical tape (20), each track (18) having an off-track threshold (22).In that regard, the optical heads (12) may be configured for bothwriting data to and reading data from the tape media (20). Thecontroller (26′) may be configured to permit, in response to an eventcausing at least one of the plurality of optical read heads (12) to havea position outside the off-track threshold (22) of the associated track(18), the read head or heads (12) to stream data when a loss of datafrom the read head or heads (12) is correctable according to the ECCdesign provided.

The controller (26′) may also be further configured to identify a defect(30) in one of the plurality of tracks (18) on the optical tape (20) andto generate a signal for use in controlling the actuator (14′)associated with the optical head (12) writing data to or reading datafrom the track (18) having the defect (30) to move the optical head (12)from the track (18) having the defect (30) to a position for readingdata from another one of the plurality of tracks (18) on the opticaltape (20). The controller (26′) may be further configured to identify afailure of a first one of the plurality of optical heads (12′) and togenerate a signal for use in controlling an actuator (14′) associatedwith a second one of the plurality of optical heads (12) to move thesecond optical head (12) to a position for reading data from or writingdata to the track (18) associated with the failed first optical head(12′).

Referring now to FIG. 4, a simplified flowchart is shown that depicts anembodiment of a method for off-track write prevention and/or datarecovery as described herein. More specifically, in an optical tapedrive comprising a plurality of optical heads for writing data in aplurality of tracks on an optical tape, each track having an off-trackthreshold, a method (40) is illustrated for off-track write prevention.The method (40) may comprise controlling (42) the plurality of opticalheads via a plurality of actuators, each actuator configured to controla position of one of the plurality of optical heads associatedtherewith, and determining (44) a position of each of the optical headsrelative to an associated track on the optical tape. The method (40) mayfurther comprise preventing (46), in response to an event causing atleast one of the plurality of optical heads to have a position outsidethe off-track threshold of the associated track, only that optical heador heads from writing data to the optical tape.

The method (40) may also comprise buffering (48) a stream of data forthat optical head or heads for later processing. As previouslydescribed, the event comprises a disturbance external to the opticaltape drive and/or motion of the optical tape in a directionsubstantially lateral to a direction of tape travel. The method (40) mayfurther comprise permitting (50), in response to the event, an opticalhead to write data to the optical tape as long as the optical head has aposition within the off-track threshold of the associated track.

As previously described, the optical tape drive may alternatively orfurther comprise a plurality of optical heads for reading data from aplurality of tracks on the optical tape, each track having an off-trackthreshold. Once again, in that regard, the optical heads may beconfigured for both writing data to and reading data from the opticaltape media. In such an embodiment, the method (40) may alternatively orfurther comprise permitting (52), in response to an event causing atleast one of the plurality of optical read heads to have a positionoutside the off-track threshold of the associated track, that read heador heads to stream data when a loss of data from that read head or headsis correctable according to the ECC design provided.

Still further, the method (40) may also comprise identifying (54) adefect in one of the plurality of tracks on the optical tape, andcontrolling (56) the actuator associated with the optical head readingdata from the track having the defect to move the optical head readingdata from the track having the defect to a position for reading datafrom another one of the plurality of tracks on the optical tape. Themethod (40) may also comprise identifying (58) a failure of a first oneof the plurality of optical heads, and controlling (60) an actuatorassociated with a second one of the plurality of optical heads to movethe second optical head to a position for reading data from or writingdata to the track associated with the failed first optical head.

Thus, in an optical tape drive system, according to the system andmethod described herein, only the heads outside their associated OTthreshold limits are prevented from processing data, and associated datamay be buffered for later processing. Thus, the data transfer rate ofthe device and the media capacity are only marginally impacted incomparison to the case where all heads are disabled for a period of timeand all data is written later. Accordingly, a smaller buffer size andlower number of sequential flushing are required for streaming data,thereby providing for a higher data transfer rate and greater mediacapacity.

As is apparent from the foregoing description, an improved system andmethod are provided for off-track write prevention and data recovery inan optical tape drive having multiple optical heads. The system andmethod overcome performance limitations associated with excessiveexternal disturbances to optical heads or excessive instantaneous tapelateral motion to provide greater data transfer rates overall andincreased data capacity.

While certain embodiments of a system and method for managing keys foruse in encrypting and decrypting data in a technology stack have beenillustrated and described herein, they are exemplary only and it is notintended that these embodiments illustrate and describe all thosepossible. Rather, the words used herein are words of description ratherthan limitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the following claims.

1-20. (canceled)
 21. In an optical tape drive comprising a plurality ofoptical heads for reading data from a plurality of tracks on an opticaltape, each track having an off-track threshold, a method for off-trackdata recovery comprising: controlling the plurality of optical heads viaa plurality of actuators, each actuator configured to control a positionof one of the plurality of optical heads associated therewith;determining a position of each of the optical heads relative to anassociated track on the optical tape; and permitting, in response to anevent causing at least one of the plurality of optical heads to have aposition outside the off-track threshold of the associated track, the atleast one optical head to stream data read from the optical tape when aloss of data from the at least one head is correctable.
 22. The methodof claim 21 wherein the event comprises a disturbance external to theoptical tape drive.
 23. The method of claim 21 wherein the eventcomprises motion of the optical tape in a direction substantiallylateral to a direction of tape travel.
 24. The method of claim 21further comprising: identifying a defect in one of the plurality oftracks on the optical tape; and controlling the actuator associated withthe optical head reading data from the tracking having the defect tomove the optical head reading data from the track having the defect to aposition for reading data from another one of the plurality of tracks onthe optical tape.
 25. The method of claim 21 further comprising:identifying a failure of a first one of the plurality of optical heads;and controlling an actuator associated with a second one of theplurality of optical heads to move the second optical head to a positionfor reading data from the track associated with the failed first opticalhead.
 26. In an optical tape drive comprising a plurality of opticalheads for writing data in a plurality of tracks on an optical tape, eachtrack having an off-track threshold, a method for off-track writeprevention comprising: controlling the plurality of optical heads via aplurality of actuators, each actuator configured to control a positionof one of the plurality of optical heads associated therewith;determining a position of each of the optical heads relative to anassociated track on the optical tape; and preventing, in response to anevent causing at least one of the plurality of optical heads to have aposition outside the off-track threshold of the associated track, onlythe at least one optical head from writing data to the optical tape. 27.The method of claim 26 further comprising buffering a stream of data forthe at least one optical head for later processing.
 28. The method ofclaim 26 wherein the event comprises a disturbance external to theoptical tape drive.
 29. The method of claim 26 wherein the eventcomprises motion of the optical tape in a direction substantiallylateral to a direction of tape travel.
 30. The method of claim 26further comprising permitting, in response to the event, an optical headto write data to the optical tape as long as the optical head has aposition within the off-track threshold of the associated track.
 31. Themethod of claim 26 wherein the optical tape drive further comprises aplurality of optical heads for reading data from a plurality of trackson the optical tape, each track having an off-track threshold, themethod further comprising permitting, in response to an event causing atleast one of the plurality of optical read heads to have a positionoutside the off-track threshold of the associated track, the at leastone read head to stream data when a loss of data from the at least oneread head is correctable.
 32. The method of claim 31 wherein the eventcomprises a disturbance external to the optical tape drive.
 33. Themethod of claim 31 wherein the event comprises motion of the opticaltape in a direction substantially lateral to a direction of tape travel.34. The method of claim 31 further comprising: identifying a defect inone of the plurality of tracks on the optical tape; and controlling theactuator associated with the optical head reading data from the trackinghaving the defect to move the optical head reading data from the trackhaving the defect to a position for reading data from another one of theplurality of tracks on the optical tape.
 35. The method of claim 31further comprising: identifying a failure of a first one of theplurality of optical heads; and controlling an actuator associated witha second one of the plurality of optical heads to move the secondoptical head to a position for reading data from the track associatedwith the failed first optical head.